A fiberoptic compatible midinfrared laser with CO2 laser-like effect: application to atherosclerosis

In theory, pulses of laser light in the 2-microns range should ablate tissue in a manner similar to that of the 10.6-microns CO2 laser with the added advantage of efficient transmission through flexible quartz fibers. Using 200-microseconds pulses of 2.15-microns thulium-holmium-chromium:YAG (THC:YAG) laser light, we were able to create 700-microns-diameter holes through calcific atherosclerosis in vitro. In vivo evaluation of thrombogenicity and healing was accomplished by exposing the luminal surface of rabbit aortas to the THC:YAG laser. Serial histologic examinations of laser-treated rabbit aortae revealed a time course of resolution of the lesions which was very similar to that observed with like-sized lesions created with the same amount of continuous wave CO2 energy. No significant differences in thrombogenicity nor healing response were noted. The excellent in vivo response observed is due in part to the pulsed nature of the THC:YAG laser output as well as to the efficient tissue absorption at the 2.15-microns wavelength. We feel that excellent ablative effects with minimal collateral thermal damage can be obtained through fiberoptic delivery systems by taking advantage of laser wavelengths corresponding to the infrared absorption peak of water in the 2-microns region and pulsed delivery of the laser energy.